When you open the faucet, that's the path of least resistance so the water will come rushing back, pushing out the air
Its drawing the water from the kitchen faucet because that is the closest fixture to the leak more than likely
It there is a complete break in the line this may be true, but if that were the case he would have water coming up through the floor or running out from under the house. If there is just a leak this is not going to happen. Also, he indicated that the original issue was pretty hard spitting and sputtering which would indicate that initially it still had pretty good pressure until the faucet stopped up (I'm guessing). If there is a break in the line that was bad enough to let air in like you are describing there would be little to no pressure and while there may be some air mixed in with, I don't believe it wouldn't have enough pressure to spit and sputter so to speak.
